1. Field of the Invention
The present invention relates to a composition based on a calcic compound, sometimes referred to herein as a powdery calco-magnesian compound.
2. Description of the Prior Art
Powdery calco-magnesian compound means a collection of solid particles, either in hydroxide form or in the form of a carbonate, complying with the following formula I:xCaA.(1−x)[yMgA+(1−y)MgO],  (I)in whichA is a ═(OH)2 or ═CO3 group, andx and y are molar fractions where 0<x≦1 and 0≦y≦1.
This calco-magnesian material obviously contains impurities, such as silica, alumina, etc, to the extent of a few percent. In general terms, the size of the particles of this powdery materials is entirely less than 1 mm and often less than 250 μm.
A particular case of a powdery calco-magnesian compound is slaked lime, also referred to as hydrated lime (calcium hydroxide—Ca(OH)2), which can also comprise impurities, such as silica, alumina, magnesium oxide or calcium carbonate, to the extent of a few percent, and contain free water, namely water not chemically bound to the compound, up to approximately 5%.
Such a compound is renowned for its lacks of flowability in flowing during storage, handling and transport, in particular pneumatic transport in dilute phase, often used in the case of slaked lime. These problems of flowing, in particular related to the fineness of the particles of the hydrated lime, exhibit themselves mainly in the form of an agglomeration of particles together or an accumulation of these on the walls. Such behaviour is detrimental to the use of said compound:                in reducing the flow rate during pneumatic transport by progressive deposition of the compound on the walls, which may go as far as the blockage of the installations,        by interfering with regulation when the compound is used as a neutraliser of acidic compounds,        requiring specific and regular maintenance operations at places which are sometimes not very accessible.        
It is known how to promote the flow of powders by means of organic liquid additives, in particular surfactants [JP 08-109016, JP 09-165 216]. However, the incorporation of such organic liquids, which are sometimes toxic, to a mineral compound such as slaked lime, is often contrary to its application, in particular in the case of use for the purification of flue gas (the problem of volatile organic compounds, following on from the release of organic additives).